A data slicer circuit for separating and recovering digital teletext data is disclosed in EP-A 144 457, corresponding to U.S. Pat. No. 4,656,513. The disclosure of U.S. Pat. No. 4,656,513 is incorporated herein by reference. According to the fundamental idea of that application and that patent, the slicing level is determined by subtracting the teletext signal from the start-value-containing composite color signal. Since the exact shape of the teletext signal is unknown or is not reproducible, a corresponding reference signal is generated and subtracted, so that an error signal is obtained. Integration of the error signal provides the unsmoothed slicing level, which still contains high-frequency interfering signals. During the generation of the reference signal, those teletext-signal amplitudes which occur shortly before and shortly after a 0 to 1 transition are suppressed, so that only the peak values of the teletext signal are evaluated.
It turns out that in teletext signals with many successive 0 to 1 transitions, i.e., zeroes, the prior art arrangement leads to unacceptable errors in the reference signal.